1. Technical Field
The present invention relates to a semiconductor device, a fabricating method thereof, and an operating method thereof, and more particularly, to a semiconductor device having a crystalline semiconductor layer, a fabricating method thereof, and an operating method thereof.
2. Discussion of the Related Art
With a highly integrated semiconductor device, channel lengths of transistors and distances, such as between transistors, are small. And as integration increases, those sizes and distances become smaller. Also, one will find with recent trends that concentrations of impurities in semiconductor substrates have increased, and thus, source/drain junction capacitances of transistors and leakage currents have increased. Consequently, the trends result in a deterioration of many other characteristics of semiconductor devices, such as high speed, low power consumption, and the like, though these properties continue to be in increasing demand.
A silicon-on-insulator (SOI) substrate is gaining attention to solve these problems. Particularly, the SOI is less susceptible to a latch up phenomenon caused by an inner feed-back phenomenon that occurs in a CMOS structure with high integration density.
The SOI substrate has a single crystal silicon layer formed on a buried insulating layer unlike a bulk silicon substrate, and an element such as a transistor is formed on the single crystal silicon layer. Generally, fabrication of the SOI substrate may be divided into two methods. A first method is a separation by implanted oxygen (SIMOX) method, in which oxygen atoms are implanted into a silicon substrate so that the oxygen atoms penetrate deep into the substrate by a predetermined depth, and an annealing process is performed to form a buried insulating layer. A second method is to form an insulating layer on a substrate and attach substrates to each other, and perform an etch-back process on the substrates.
A main drawback, however, of the first method is that its processes are complicated and inconvenient because a LOCOS process or an STI process must be performed to form an isolation layer after oxygen ions are implanted into a silicon substrate, and a thermal treatment process is performed. Furthermore, serious defects may be generated inside the semiconductor substrate on which elements will be formed. In the second method, however, since two substrates having an insulating layer formed thereon are attached at a high temperature, and one side of the substrates is polished, it is required to perform a thermal treatment process at a high temperature, and voids may be generated at the junction portion of the substrates.
Recently, as one of the efforts to solve these problems, a method of fabricating an SOI substrate is disclosed in U.S. Pat. No. 6,602,758 B2 in the title of “Formation of Silicon On Insulator Devices as Add-On Modules for System On a Chip Processing” to Kizilyalli, et al. According to Kizilyalli, et al., an insulating layer is formed on a semiconductor substrate, and the insulating layer is patterned, thereby forming an opening exposing the semiconductor substrate. An amorphous silicon layer is formed on the patterned insulating layer to contact the exposed semiconductor substrate, and an eximer laser is applied to crystallize the amorphous silicon layer. As a result, a silicon layer having substantially the same single crystal structure as that of the semiconductor substrate is formed.
However, a continuous effort is required to fabricate an improved semiconductor device using a crystalline semiconductor layer formed on the semiconductor substrate as well as to form the SOI substrate.